Born in Pittsburgh, Pennsylvania, of Polish descent, the daughter of Walter Joseph and Regina Mary (Pilarska) Los.

Mansmann received a Bachelor of Arts degree from Duquesne University in 1964 and a Juris Doctor from Duquesne University School of Law in 1967, one of only two women to graduate that law school in 1967.

She was in private practice in Pittsburgh from 1973 to 1979, and was also a special assistant to the Attorney General of Pennsylvania from 1974 to 1979.

[1] Mansmann was nominated by President Reagan on March 7, 1985, to the United States Court of Appeals for the Third Circuit, to a new seat authorized by 98 Stat.

[1] Mansmann died of breast cancer (with which she had initially been diagnosed in 1989) at UPMC Montefiore, Pittsburgh, on March 9, 2002, aged 59.